Jelly- the Cartesian diver: Make your own straw diver!

Jelly is a magical straw diver (it sinks when you squeeze its container and floats when you release it).

This experiment will enabe a fun learning of the buoyancy concept and the ideal gas law

What you need:

1)An empty & clear plastic bottle. 2)Water. 3)drinking straw. 4)A pair of scissors. 5)A split shot sinker.

Instructions

1) Fill the bottle with water till it is almost full. 2) Use scissors to cut about 2” off the straw. 3) Bend the straw to make a U shape. Ensure that the ends of the folded straw are equal. 4) Use a split shot sinker to clip the two ends of the straw together on the sides that are touching. Leave a space for water to go inside the straw. 5) Drop the straw into the bottle and check if it floats. If it does, your “straw diver” is ready and you can move to step 6. If it does not, repeat step 4 making sure that there is a space for water. 6) Put the cap and close the bottle. 7) Squeeze and release the bottle. When you squeeze the bottle, your straw diver should sink and when you release it, your straw diver should float.

Explanation

Initially, the straw (diver) floats because its overall density is less than that of the surrounding water. When the bottle is squeezed, the pressure on the water and on the air bubble (originally trapped inside the straw) increases. Water is forced into the straw and compresses the air bubble into a smaller volume. With more water inside the straw, its overall density increases and the straw (diver) sinks once its density becomes higher than that of the surrounding water. When you release the bottle, the air bubble expands to its initial volume and pushes the water out of the straw causing the diver to float.